1. Field of the Invention
The present invention relates to engineered cementitious composites (ECCs), and particularly to a fire resistant cementitious composite including polyvinyl alcohol (PVA) fibers and dune sand.
2. Description of the Related Art
Engineered cementitious composites (ECCs), also referred to as “bendable concrete”, are easily molded, mortar-based composites reinforced with specially selected short random fibers, typically in the form of polymer fibers. Unlike regular concrete, ECCs have a strain capacity in the range of 1-7%, compared to 0.1% for ordinary Portland cement (OPC). ECCs thus act more like a ductile metal than a brittle glass (as does OPC concrete), leading to a wide variety of applications.
ECCs have a variety of unique properties, including tensile properties superior to other fiber-reinforced composites, ease of processing on par with conventional cement, the use of only a small volume fraction of fibers (˜2%), tight crack width, and a lack of anisotropically weak planes. These properties are due largely to the interaction between the fibers and cementing matrix, which can be custom-tailored through micromechanics design. Essentially, the fibers create many microcracks with a very specific width, rather than a few very large cracks (as in conventional concrete). This allows ECCs to deform without catastrophic failure.
Despite the desirable properties of ECCs, the fire-resistance of conventional ECCs is questionable, and particularly a matter of concern when non-metallic fibers are used in the ECC. The most common non-metallic fibers used in ECCs are polyvinyl alcohol (PVA) fibers, forming an ECC reinforced with PVA (ECC-PVA). It is well known that the melting point of PVA fibers onsets at about 200° C. and their thermal decomposition starts approximately at 239° C. At this temperature, PVA fibers in ECC-PVA are thermally decomposed and gases evolve. During these stages of thermal degradation, different types of voids and deterioration mechanisms are created which substantially affect the strain-hardening and hardened properties of the ECC-PVA. Thus, there is a need for a cost-effective method of increasing the thermal resistivity of the PVA in FCC-PVA at higher temperatures. Particularly, it would be desirable to be able to modify the structure of the PVA in the ECC-PVA to provide both flexural strength and to prevent explosive spalling at high temperatures.
Explosive spalling takes place once the accumulated vapor pressure inside the ECC-PVA reaches stresses surpassing its tensile strength. Explosive spalling relies mainly on both pore water content and tensile strength. Generally, at a temperature of 400° C., PVA fibers char and turn into a residue of carbon while the cementitious matrix itself begins thermal decomposition. It would obviously be desirable to minimize these effects at such a critical temperature, yielding not only a cost-effective ECC-PVA with flexural strength, but also being thermally resistant without explosive spalling. Thus, a fire resistant cementitious composite and method of making the same solving the aforementioned problems is desired.